1. Field of the Invneiton
The present invention relates to an electrophotographic photosensitive member, and, particularly, to a function-separated type electrophotographic photosensitive member improved in image stability and potential stability.
2. Related Background Art
As electrophotographic photosensitive members comprising inorganic photoconductive materials, conventionally used are those employing selenium, cadmium sulfide, zinc oxide and so forth.
As electrophotographic photosensitive members comprising organic photoconductive materials, on the other hand, known are those employing a photoconductive polymer typified by poly-N-vinyl carbazole or a low molecular organic photoconductive material such as 2,5-bis(p-diethylaminophenol)-1,3,4-oxadiazole, or those wherein such organic photoconductive materials are combined with a variety of dyes or pigments.
The electrophotographic photosensitive members employing organic photoconductive materials are advantageous in that they have good film-forming properties and can be produced by coating to have very high productivity to provide photosensitive members inexpensively. They are also advantageous in that the color-sensitivity can be controlled as desired, by selecting sensitizers such as dyes or pigments to be used, and therefore studies have hitherto been made in a wide range. Particularly in recent years, function-separated type photosensitive members employing an organic photoconductive pigment in a charge generation layer and laminated with a so-called charge transport layer comprising the above photoconductive polymer or low molecular organic photoconductive material, have been developed to have remarkably improved the sensitivity and durability in which the conventional organic electrophotographic photosensitive members have been considered defective, and they have been put into practical use. Moreover, various compounds and pigments suited to the function-separated type photosensitive members have been discovered.
However, such function-separated type photosensitive members are disadvantageous in that a charge transporting material present in the charge transport layer constituting the surface layer of the photosensitive member is subject to adsorption of, or oxidation by, active components such as ozone generated by corona discharge, to cause a blur of an image when used repeatedly or cause a background fog of an image due to the accumulation of residual potential.